The present invention relates generally to a Light Emitting Diode (LED) driver and, more specifically, to a single-stage non-isolated switching converter capable of high-efficiency operation, low harmonic distortion of the AC line current, high reliability and long life in the presence of an elevated ambient temperature.
Recent developments of high-brightness light emitting diodes (LED) have opened new horizons in lighting. Highly efficient and reliable LED lighting continuously wins recognition in various areas of general lighting, especially in areas where cost of maintenance is a concern. One example of such application is in street lighting where LED lighting is becoming increasingly popular throughout the world.
These applications have created demand for a special LED driver, a current-regulated power supply circuit, which can match the long life of LEDs. A typical set of requirements to such LED driver includes high power efficiency, power factor correction (PFC) and low distortion of the input AC current. Due to high power dissipation within LEDs themselves, the LED driver must be capable of continuous operation at elevated ambient temperature. Non-isolated LED driver topologies are typical for these types of applications, since galvanic safety isolation of the LED load from AC mains is not generally required.
However, prior art LED drivers generally employ two-stage power conversion, wherein the first stage, typically a boost converter, is responsible for AC-to-DC rectification featuring power factor correction and low harmonic distortion of the AC line current, and the second stage is a constant output current DC-to-DC converter. One obvious disadvantage of such approach is its higher cost and component count compared to a single-stage power supply. Since the overall efficiency of such an LED driver is the product of the efficiency of each conversion stage, achieving high efficiency can be difficult with a two-stage approach.
Therefore, it would be desirable to provide a circuit and method that overcomes the above problems. The circuit would be a single-stage non-isolated switching converter capable of high-efficiency operation, low harmonic distortion of the AC line current, high reliability and long life in the presence of an elevated ambient temperature.